1. Field of the Invention
The present invention relates to a core sheet, core and method of manufacturing an armature using the core sheet.
2. Related Art
In a conventional electric motor, as shown in FIGS. 19, 20, 21, an armature 20 has a rotary shaft SH at its radial center. A core 21 wound with armature windings C is fixed to the rotary shaft SH together with commutator SG. The core 21 comprises a plurality of stacked core sheets 22, each of which is a thin magnetic steel plate. The core 21 has on its outer peripheral surface a plurality of slits 23, each of which extends in parallel with the rotary shaft SH. The slit 23 has a slit width d in the circumferential direction of the core 21.
The core sheet 22 has a plurality of T-shaped teeth 24 extending in the radial direction from its radial central part. The core sheet 22 also has a through hole 25 at its central part so that the rotary shaft SH passes therethrough in the axial direction. The teeth 24 are spaced apart in the circumferential direction to provide a plurality of slots 26.
Each armature winding C is wound around each tooth 24 through slits 23. Specifically, the armature winding C is wound in the slots 26 from the radial central part toward the outer peripheral part of the core 21 in generally the fixed width d.
In this armature 20, there remains in each slot 26 space at a location other than the space corresponding to the slit width d, because the space for disposing the armature winding C is limited by the slit width d. Thus, the space in the slot 26 is not used effectively.
It is possible to wind the armature winding in more turns in the slot 26 by widening the slit width. However, the widened slit is likely to cause cogging in the torque of the motor, because each slit 23 extends in the axial direction as a continuous line thereby causing reluctance changes at the same time. Further, the slipping out of the armature winding c is likely to occur in the radially outward direction from the slot 26 through the slit. Thus, the width of the slot should not be widened too much.